The invention relates to a vacuum toilet comprising a bowl with flushing nozzles mounted in the upper area of the bowl and a shutoff valve in the waste pipe connected in the lower area of the bowl.
In vacuum toilets of this type operating conditions may occur which are highly undesirable and in some cases may have disastrous consequences.
If, for example, delivery of flushing water to the flushing nozzles is not shut off because of an error of some nature, the flushing water flows into the bowl and cannot drain downwards, since the shutoff valve is closed. In this instance the water level in the bowl rises and a situation may finally arise in which the flushing nozzles come in contact with the waste water in the bowl, with the result that undesirable contact of more or less polluted waste water to the fresh water circulation may occur; for example, should a defect in the fresh water system cause suction to occur, polluted water from the toilet could reach the fresh water system. But this must be prevented. The safety measure applied in this case would be installation of a separate flushing water circuit in addition to the fresh water circuit, that is, a relatively cost intensive measure.
It is also conceivable that, in instances of improper use of state-of-the-art vacuum toilets, in particular ones used in aircraft, for which the negative pressure outside an airplane flying at a high altitude is used as a means of conveyance, the suction action of the vacuum might draw in objects or human body parts so that the danger of damage to objects and of serious physical injury exists.